A device that was capable of detecting living tissue within a set radius.

This device was able to sense the presence of life directly, without using auxiliary signs (like carbon dioxide or heat emission).

The antennae of the Life Detector atop the OP swept back and forth in a rhythmic halfcircle like so many frozen sticks brittle with rime ice...

One operator - drugged to shivering wakefulness - stood watch in the OP. The space around him was barely six feet in diameter, crammed with equipment, gridded screens glowing a pale green with spots that indicated living flesh: a covey of ptermigan, a possible Artic fox. Every grid point on the screens held an aiming code for mortar fire.